1. Field of the Invention
This invention relates to photothermographic elements, compositions and processes for providing a developed image in color by heating the element or composition after imagewise exposure. In one of its aspects, it relates to a photothermographic element for providing such a developed image in color containing certain leuco-base dyes in association with (a) photographic silver halide with (b) an oxidation reduction image-forming combination comprising (i) a silver salt oxidizing agent, with (ii) an organic reducing agent. In another of its aspects, it relates to a photothermographic composition containing the described components. A further aspect relates to a diffusion transfer photothermographic element containing the described combination of components with an image-receiving layer. A further aspect relates to a process of developing an image in color in an imagewise exposed photothermographic element as described by heating the element.
2. Description of the State of the Art
It is well known to develop a latent image in a photothermographic element by so-called processing with heat. After imagewise exposure, the resulting latent image in the photothermographic element is developed by heating the photothermographic element. Such photothermographic elements and processes are described, for example, in U.S. Pat. No. 3,152,904 of Sorensen et al, issued Oct. 13, 1964; U.S. Pat. No. 3,301,678 of Humphlett et al, issued Jan. 31, 1967; U.S. Pat. No. 3,392,020 of Yutzy et al, issued July 9, 1968; U.S. Pat. No. 3,457,075 of Morgan et al, issued July 22, 1969; British Pat. No. 1,131,108, published Oct. 23, 1968; German Pat. No. 888,045, issued June 29, 1943 and British Pat. No. 1,161,777 published Aug. 20, 1969.
Certain photographic materials for producing a developed image in color by so-called processing with heat are described, for example, in U.S. Pat. No. 3,531,286 of Renfrew, issued Sept. 29, 1970. Other photothermographic materials for producing an image in color by heating a photothermographic element are described in U.S. Pat. No. 3,761,270 of deMauriac et al, issued Sept. 25, 1973. The photothermographic materials described in these patents employ color-forming couplers which react with oxidized reducing agents to provide a dye image. It has been desirable to avoid the use of color-forming couplers in photothermographic materials because the color-forming couplers have been thought to require a relatively high pH, e.g. 8-13, to provide a desired coupling reaction. It has also been desirable to avoid base-release agents which have been used to provide the desired pH for the coupling reaction in these photothermographic materials. However, no suitable solution for eliminating the need for color-forming couplers and base-release agents in photothermographic materials of the described type is evident from the art. Also, in some cases, employing color-forming couplers with para-phenylenediamine developing agents in photothermographic materials to form color images provides undesired spontaneous reduction of, for example, silver behenate, in the presence of the color-developing agent.
Other photothermographic materials are known. These can comprise certain dyes and are illustrated by those materials described in U.S. Pat. No. 3,007,795 of Haydn et al, issued Nov. 7, 1961; U.S. Pat. No. 3,346,382 of VonKonig et al, issued Oct. 10, 1967; U.S. Pat. No. 3,383,212 of MacLochlan, issued May 14, 1968; U.S. Pat. No. 3,390,995 of Manos, issued July 2, 1968; German OLS No. 2,117,053 of Agfa-Gevaert, issued Nov. 4, 1971 and U.S. Pat. No. 3,180,731 of Roman et al, issued Apr. 27, 1965. These photothermographic materials have not provided answers to the problem of producing a photothermographic element and composition comprising photographic silver halide in association with an oxidation-reduction image-forming combination which provides a desired color image.
Thermographic materials are also known in which an image is produced by imagewise heating the material, rather than imagewise exposing the material to light followed by overall heating the material. These thermographic materials lack the photographic capability of photothermographic materials containing photographic silver halide. Typical thermographic materials are described, for example, in U.S. Pat. No. 3,409,457 of Menzel, issued Nov. 5, 1968; U.S. Pat. No. 3,447,944 of Werner, issued June 3, 1969; and U.S. Pat. No. 3,663,258 of Wiese et al, issued May 16, 1972.
There has been a continuing need to provide photothermographic elements, compositions and processes for producing a color image wherein the photothermographic element or composition comprises photographic silver halide in association with a so-called oxidation-reduction image-forming combination and a development modifier without the need of a color-forming coupler and a base-release agent.